1. Field of the Invention
The invention relates to a pressure regulator for hydraulic vehicle braking systems, comprising a casing which has an inlet and a valve chamber connected to the same as well as an outlet, a valve seat which is arranged in the valve chamber at the entrance of a passage leading to the outlet, and a valve member which is arranged in the valve chamber so that brake fluid can flow around it and which is movable in response to deceleration from an inoperative position to the valve seat.
2. Description of the Prior Art
A pressure regulator of this kind known from DE-C No. 1 780 644 has the valve chamber limited rearwardly toward the inlet by a partition which fixes the inoperative position of the valve member embodied by a sphere. The partition separates the valve chamber from an antechamber which communicates with the inlet through a constricted axial passage. A jet-like hole is formed in the middle of the partition and, upon vigorous brake actuation, brake fluid will flow like a jet through this hole against the valve member imparting to the latter an impulse to propel it against the valve seat. In this manner it is assured that the valve member quickly blocks the passage leading to the outlet if the brakes are actuated suddenly or especially strongly, thus preventing jamming of the rear wheel brakes which are connected to the outlet. Upon smooth and gradual brake actuation, on the other hand, the valve closing member will not reach the valve seat until the deceleration of the vehicle equipped with the pressure regulator has surpassed a certain value. A stepped bore is connected in parallel with the valve chamber and the passage leading from the same to the outlet. In this bore a stepped piston is so arranged that its smaller end surface is exposed to the pressure prevailing at the inlet and its greater end surface to the pressure at the outlet. Upon closing of the valve and further pressure rise at the inlet, therefore, the stepped piston causes a reduced pressure increase at the outlet.
Another pressure regulator of the kind specified initially is known from DE-C No. 2 213 463 with which the passage leading from the valve chamber to the outlet is formed in a stepped piston whose smaller end surface defines the valve chamber and carries the valve seat. Also with this known pressure regulator the valve member constituted by a sphere comes to lie against the valve seat at a certain deceleration of the vehicle, thus blocking the passage which leads to the outlet. As the pressure continues to rise at the inlet and in the valve chamber, the stepped piston is displaced forwards into a position into which the valve member cannot follow because an annular stop at the casing prevents its further forward movement. Therefore, more brake fluid flows through the passage in the stepped piston to the outlet where it causes a further increase in pressure which again moves the stepped piston to the rear so that the valve seat once more contacts the valve member. These reciprocating motions of the stepped piston are repeated as the pressure continues to rise. After the first closing of the valve, therefore, the pressure at the outlet increases less steeply than the pressure at the inlet, as with the known pressure regulator described first.
With this and further known pressure regulators of this kind there is a possibility, for instance, after an exchange of the brake fluid that an air bubble forms in the highest region of the valve chamber above and in front of the valve seat. It would be costly to provide a vent screw at this location and, besides, such a vent screw would be difficult to reach with the usual conditions of installation. Thus it would be desirable to vent a braking system comprising one or more pressure regulators of the kind specified at a different place, preferably located centrally and readily accessible. To achieve that, it is a condition that air bubbles be dispelled from the valve chamber toward the outlet, a place from which they will easily reach the central venting location if suitable conduits are provided. For safety reasons this must be done with the vehicle at standstill, i.e. without the cooperation of forces of deceleration.
With the pressure regulator known from DE-C No. 1 780 644 a liquid fet directed against the valve member can be produced upon violent brake actuation, and this jet is suitable to move the valve member forwardly into a position in which it constricts the space taken up by an air bubble. Yet the liquid jet is not sufficient to cause a flow between the valve member and the valve seat strong enough to entrain the air bubble. With the pressure regulator known from DE-C No. 2 213 463 strong brake actuation with the vent screw at a communicating rear wheel brake in open position, can convey a great amount of brake fluid per unit time into the valve chamber because the latter is connected directly to the inlet. However, with the vehicle stopped, the valve member cannot be moved forwards and, therefore, cannot define an annular space around the valve seat narrow enough to create a flow velocity at which air is entrained.